1. Field of the Invention
The present invention is related to a gain amplifier, in particular, to a linear programmable switch-capacitance gain amplifier (PGA).
2. Description of Related Art
A commonly used linear programmable switch-capacitance gain amplifier (PGA) employs
      1    +    x        1    -    x  for approximating operations. In case of applications requiring wider range of adjustment and better precision, the entire linear programmable switch-capacitance gain amplifier will be divided into two or more parts, as shown in FIG. 7, which illustrates an architecture of a prior art linear programmable switch-capacitance gain amplifier using 2 parts of operation, as well as shown in FIG. 8, which illustrates an architecture of a prior art linear programmable switch-capacitance gain amplifier using several parts of operation. At the stage of Least Significance Bits (LSB), it generally uses the approximately linear
      1    +    x        1    -    x  for implementing 0-6 dB, from which the derived maximum error will be about −0.09 dB, as shown in FIG. 9, which shows a diagram representing the error in a prior art linear programmable switch-capacitance gain amplifier. However, even though the error is of small magnitude, there exists a disadvantage in that such a linear programmable switch-capacitance gain amplifier needs at least one more gain stage.